U.S. patent number 9,583,776 [Application Number 14/241,569] was granted by the patent office on 2017-02-28 for sweep membrane separator and fuel processing systems.
This patent grant is currently assigned to BATTELLE MEMORIAL INSTITUTE. The grantee listed for this patent is Vincent J. Contini, Paul E. George, II, Douglas A. Thornton. Invention is credited to Vincent J. Contini, Paul E. George, II, Douglas A. Thornton.
United States Patent |
9,583,776 |
Thornton , et al. |
February 28, 2017 |
**Please see images for:
( Certificate of Correction ) ** |
Sweep membrane separator and fuel processing systems
Abstract
A sweep membrane separator includes a membrane that is
selectively permeable to a selected gas, the membrane including a
retentate side and a permeate side. A mixed gas stream including
the selected gas enters the sweep membrane separator and contacts
the retentate side of the membrane. At least part of the selected
gas separates from the mixed gas stream and passes through the
membrane to the permeate side of the membrane. The mixed gas
stream, minus the separated gas, exits the sweep membrane
separator. A sweep gas at high pressure enters the sweep membrane
separator and sweeps the selected gas from the permeate side of the
membrane. A mixture of the sweep gas and the selected gas exits the
sweep membrane separator at high pressure. The sweep membrane
separator thereby separates the selected gas from the gas mixture
and pressurizes the selected gas.
Inventors: |
Thornton; Douglas A. (Columbus,
OH), Contini; Vincent J. (Powell, OH), George, II; Paul
E. (Powell, OH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Thornton; Douglas A.
Contini; Vincent J.
George, II; Paul E. |
Columbus
Powell
Powell |
OH
OH
OH |
US
US
US |
|
|
Assignee: |
BATTELLE MEMORIAL INSTITUTE
(Columbus, OH)
|
Family
ID: |
46982917 |
Appl.
No.: |
14/241,569 |
Filed: |
August 31, 2012 |
PCT
Filed: |
August 31, 2012 |
PCT No.: |
PCT/US2012/053331 |
371(c)(1),(2),(4) Date: |
June 23, 2014 |
PCT
Pub. No.: |
WO2013/033529 |
PCT
Pub. Date: |
March 07, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150147668 A1 |
May 28, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61530723 |
Sep 2, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
19/245 (20130101); H01M 8/0675 (20130101); B01D
53/229 (20130101); B01J 19/24 (20130101); H01M
8/12 (20130101); C01B 3/34 (20130101); H01M
8/0618 (20130101); C01B 3/501 (20130101); C10G
67/06 (20130101); C10G 45/02 (20130101); C01B
3/503 (20130101); C01B 2203/0475 (20130101); H01M
2008/1293 (20130101); C01B 2203/0227 (20130101); C01B
2203/048 (20130101); B01D 2053/221 (20130101); C01B
2203/0405 (20130101); C01B 2203/127 (20130101); C01B
2203/0822 (20130101); Y02E 60/50 (20130101); C01B
2203/0205 (20130101); B01J 2219/24 (20130101); C01B
2203/066 (20130101); C01B 2203/047 (20130101); C01B
2203/1235 (20130101); H01M 2300/0074 (20130101) |
Current International
Class: |
H01M
8/06 (20160101); C10G 45/02 (20060101); C01B
3/50 (20060101); C01B 3/34 (20060101); C10G
67/06 (20060101); H01M 8/12 (20160101); B01J
19/24 (20060101); B01D 53/22 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0320979 |
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Dec 1988 |
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EP |
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2002356308 |
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Dec 2002 |
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JP |
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2006084664 |
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Mar 2006 |
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JP |
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2009150679 |
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Dec 2009 |
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WO |
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2010056829 |
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May 2010 |
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WO |
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2011033280 |
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Mar 2011 |
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WO |
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Other References
International Search Report, Application No. PCT/US2011/056129
dated Sep. 5, 2012. cited by applicant .
PCT International Search Report and Written Opinion, Application
No. PCT/US2012/053331, dated Mar. 27, 2013. cited by applicant
.
PCT Invitation to Pay Additional Fees and, Where Applicable,
Protest Fees, date of mailing Jul. 2, 2012. cited by applicant
.
Written Opinion of the International Searching Authority,
Application No. PCT/US2011/056129 dated Sep. 5, 2012. cited by
applicant.
|
Primary Examiner: Alejandro; Raymond
Attorney, Agent or Firm: MacMillan, Sobanski & Todd,
LLC
Claims
The invention claimed is:
1. A fuel pre-processing system including: a hydrodesulfurization
reactor operating at a pressure of 200-500 psig and a temperature
of 200-500.degree. C., for performing vapor-phase
hydrodesulfurization of a sulfur-bearing hydrocarbon fuel, to
produce a product stream including clean fuel and hydrogen sulfide;
a sulfur compound absorbing reactor operating at a pressure of
200-500 psig and a temperature of 200-400.degree. C., connected
downstream from the hydrodesulfurization reactor, for adsorbing the
hydrogen sulfide from the product stream; a supply of the
sulfur-bearing hydrocarbon fuel connected upstream from the
hydrodesulfurization reactor, to provide the sulfur-bearing
hydrocarbon fuel for the hydrodesulfurization reaction; and a sweep
membrane separator connected upstream from the hydrodesulfurization
reactor to provide hydrogen for the hydrodesulfurization reaction,
the sweep membrane separator including a membrane that is
selectively permeable to hydrogen, the hydrogen provided by the
sweep membrane separator being at a pressure equal to or greater
than the hydrodesulfurization reactor operating pressure.
2. The fuel pre-processing system of claim 1 further comprising a
reforming reactor connected upstream from the sweep membrane
separator, the reforming reactor producing a reformate which is fed
to the sweep membrane separator, the reformate including hydrogen,
the sweep membrane separator separating at least part of the
hydrogen from the reformate and pressurizing the separated
hydrogen, the hydrodesulfurization reactor being operated at a
higher pressure than the reforming reactor.
3. The fuel pre-processing system of claim 2 wherein the reforming
reactor is supplied by a burner to provide heat for reforming.
4. The fuel pre-processing system of claim 3 wherein the burner
operates on excess reformate or off-gas from the
hydrodesulfurization process.
5. The fuel pre-processing system of claim 2 wherein the reforming
reactor is a microtech type reactor.
6. The fuel pre-processing system of claim 2 wherein the reforming
reactor is designed for high heat transfer from the combustion
gases.
7. The fuel pre-processing system of claim 2 further comprising a
primary water vaporizer to supply the reforming reactor.
8. The fuel pre-processing system of claim 1 further comprising a
secondary water vaporizer to supply the sweep separator.
9. The fuel pre-processing system of claim 2 further comprising a
clean fuel output which is directed to the reforming reactor
without being condensed.
10. The fuel pre-processing system of claim 2 further comprising a
clean fuel output, some portion of the clean fuel outlet being
directed to the reforming reactor without being condensed, and some
portion of the clean fuel output being directed to a fuel condenser
for storage or distribution.
11. The fuel pre-processing system of claim 2 wherein the sweep
membrane separator comprises: the membrane that is selectively
permeable to hydrogen, the membrane including a retentate side and
a permeate side; a stream of the reformate entering the sweep
membrane separator and contacting the retentate side of the
membrane; at least part of the hydrogen separating from the
reformate and passing through the membrane to the permeate side of
the membrane; the reformate, minus the separated hydrogen, exiting
the sweep membrane separator; a sweep gas at high pressure entering
the sweep membrane separator and sweeping the hydrogen from the
permeate side of the membrane; and a mixture of the sweep gas and
the hydrogen exiting the sweep membrane separator at high pressure;
the sweep membrane separator thereby separating hydrogen from the
reformate and pressurizing the hydrogen.
12. The fuel pre-processing system of claim 2 wherein the
hydrodesulfurization reactor operates at a pressure of 250-500
psig.
13. The fuel pre-processing system of claim 2 wherein the
hydrodesulfurization reactor operates at a pressure of 270-500
psig.
14. The fuel pre-processing system of claim 2 further comprising a
connection between the sweep membrane separator and the supply of
sulfur-bearing hydrocarbon fuel, so that the hydrogen from the
sweep membrane separator and the fuel from the fuel supply are
mixed together before being fed to the hydrodesulfurization
reactor.
15. The fuel pre-processing system of claim 2 wherein the sulfur
compound absorbing reactor contains zinc oxide.
16. The fuel pre-processing system of claim 1 wherein the sweep
membrane separator comprises: the membrane that is selectively
permeable to hydrogen, the membrane including a retentate side and
a permeate side; a mixed gas stream including the hydrogen entering
the sweep membrane separator and contacting the retentate side of
the membrane; at least part of the hydrogen separating from the
mixed gas stream and passing through the membrane to the permeate
side of the membrane; the mixed gas stream, minus the hydrogen,
exiting the sweep membrane separator; a sweep gas at high pressure
entering the sweep membrane separator and sweeping the hydrogen
from the permeate side of the membrane; and a mixture of the sweep
gas and the hydrogen exiting the sweep membrane separator at high
pressure; the sweep membrane separator thereby separating the
hydrogen from the gas mixture and pressurizing the hydrogen.
17. The fuel pre-processing system of claim 16 wherein the sweep
gas is steam.
18. The fuel pre-processing system of claim 16 wherein the mixed
gas stream is a reformate in a hydrocarbon fuel processing
system.
19. The fuel pre-processing system of claim 16 wherein the sweep
gas is a vaporized fuel.
Description
BACKGROUND OF THE INVENTION
This invention relates in general to membrane separators and to
fuel processing systems.
In the field of hydrocarbon fuel processing, a need exists for
efficient ways to reduce organic sulfur components and other
contaminants. An example of the need for new desulfurization
approaches involves power generation. One promising technology is
fuel cells, which can provide a silent source of power having a low
heat signature. However, most fuel cells require hydrogen or a
hydrogen-rich gaseous mixture as fuel. Short of providing stored
hydrogen gas, the primary means of supplying hydrogen is by
reforming a hydrocarbon fuel. Both liquid and gaseous fuels may be
reformed, with liquid fuels typically being more difficult due to
more complex molecules and contained contaminants.
The fuel input to a liquid fueled fuel cell system must generally
be free of specific contaminants, the most problematic being
sulfur. However, liquid hydrocarbon fuels generally contain sulfur
levels that are too high for direct use in fuel cells. For example,
typical military and aviation fuel specifications allow up to 3000
ppm in JP8, JP5, and Jet-A. These are all common aircraft fuels,
the first two being exclusively military fuels. Gasoline, diesel
and heating fuels in the US have lower sulfur limits (15 ppmw), but
the allowed and typical sulfur levels are still above those
acceptable to fuel cell systems including most reforming
technologies.
Current technologies for removing sulfur from liquid hydrocarbon
feedstocks include hydrodesulfurization (HDS), a technology well
known in the commercial world. Most commonly, HDS is carried out
with hydrogen gas at high pressure being passed over a liquid
hydrocarbon fuel in a cascade or trickle bed reactor. In a separate
invention, Battelle Memorial Institute has developed an HDS system
wherein a hydrogen-containing gaseous mixture, with the hydrogen at
high partial pressure, is mixed with vaporized raw fuel and put in
contact with a selective catalyst (see U.S. patent application No.
2009/0035622 A1, published Feb. 5, 2009, which is incorporated by
reference herein). In both systems, the sulfur in the fuel then
combines with the hydrogen, freeing itself from the fuel and
becoming primarily gaseous hydrogen sulfide. The hydrogen sulfide
can then be absorbed or removed by other means.
There is a need for an improved apparatus for supplying hydrogen at
high pressure for use in HDS systems and other applications. There
is also a need for improved fuel processing systems including such
an apparatus. More generally, there is a need for an improved
apparatus for supplying pressurized gases for many different
applications.
SUMMARY OF THE INVENTION
A sweep membrane separator includes a membrane that is selectively
permeable to a selected gas, the membrane including a retentate
side and a permeate side. A mixed gas stream including the selected
gas enters the sweep membrane separator and contacts the retentate
side of the membrane. At least part of the selected gas separates
from the mixed gas stream and passes through the membrane to the
permeate side of the membrane. The mixed gas stream, minus the
separated gas, exits the sweep membrane separator. A sweep gas at
high pressure enters the sweep membrane separator and sweeps the
selected gas from the permeate side of the membrane. A mixture of
the sweep gas and the selected gas exits the sweep membrane
separator at high pressure. The sweep membrane separator thereby
separates the selected gas from the gas mixture and pressurizes the
selected gas. In certain embodiments, the sweep gas is steam and
the selected gas is hydrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a fuel processing system that can
be used to provide high purity hydrogen to a fuel cell stack, and
that includes several improved features described herein, but that
does not include a sweep membrane separator to supply hydrogen to
the HDS system.
FIG. 2 is a schematic diagram of a fuel processing system that
includes a sweep membrane separator according to the invention. In
this system the fuel is not condensed before entering the
reformer.
FIG. 3 is a schematic diagram of another fuel processing system
that includes a sweep membrane separator according to the
invention. In this system the fuel is condensed and then supplied
to a reformer for normal operation.
FIG. 4 is a schematic diagram of a fuel processing system for a
solid oxide fuel cell that includes a sweep membrane separator
according to the invention, and that does not include a large
membrane separator or a water-gas shift reactor.
FIG. 5 is a schematic diagram of a sweep membrane separator in
operation according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a sweep membrane separator
suitable for supplying pressurized gases for many different
applications, such as supplying hydrogen at high pressure for use
in an HDS reactor in a fuel processing system. It also relates to
different embodiments of fuel processing systems including the
sweep membrane separator. The invention can be used with all
different types of fuel cells, such as PEM (proton exchange
membrane), SOFC (solid oxide fuel cells), phosphoric acid, molten
carbonate, or alkaline fuel cells.
The invention further relates to various features of fuel
processing systems that do not include the sweep membrane
separator. For example, FIG. 1 shows a basic system schematic for a
fuel processing system that can be used to provide high purity
hydrogen to a fuel cell stack. Some examples of features shown in
FIG. 1 include the following: A slipstream of reformate is directed
to the HDS system prior to the shift reactor. Water is condensed
from the reformate prior to the HDS system. The reformate is
recuperated to elevated temperature after the condenser. Fuel
leaving the HDS system is passed over a ZnO bed which removes most
sulfur species but may not remove sulfur carbonyl (COS), a possible
byproduct of the HDS reaction due to the presence of CO and
CO.sub.2 in the reformate. After the HDS system and ZnO bed, the
clean fuel is condensed before being supplied to the reformer. In
the embodiment shown, the condensed fuel is transferred to a clean
fuel storage tank for future use by the reformer, but alternatively
it could be directed immediately to the reformer.
In an example of a fuel processing system similar to that shown in
FIG. 1, the system can generate clean, desulfurized fuel that is
then used in the system for both the fuel cell supply and to clean
up raw, high-sulfur fuel using gas phase hydrodesulfurization. An
example of operating conditions for the HDS reactors is about 280
psig and 380.degree. C. These conditions may also be used for the
ZnO bed although slightly cooler temperatures may be preferred.
Typically the hot fuel/hydrogen mix leaving the ZnO bed would be
recuperated to preheat another cooler stream (not shown) before
being directed to the condenser. The reformate not consumed in the
HDS process is separated in the condenser and routed to the
combustor for a steam reformer to make use of the residual chemical
energy. Because reformate is used to desulfurize the fuel in FIG.
1, the clean fuel must be at lower pressure than the reformer feed
and it is more efficient to condense and pump the fuel than to
attempt to compress the hot fuel/reformate mixture to supply it
directly to the reformer.
FIG. 2 shows a fuel processing system similar to that shown in FIG.
1 but further including a sweep membrane separator according to the
invention (referred to in the figure as a "Sweep Separator"). In
this system, the clean fuel does not need to be condensed before
entering the reformer. This simplifying feature is available
because the inclusion of the sweep separator allows the HDS system
to be operated at a higher pressure than the reformer. Some
examples of features shown in FIG. 2 include the following: The
fuel condenser and associated hardware are shown dashed to indicate
that they are not needed. Typically this hardware may be included
in a complete system to produce clean liquid fuel to support
start-up, but this hardware is not needed for normal operation and
if included can be substantially smaller since it only needs to
produce a small amount of fuel. A second, but smaller water
vaporizer has been added. A second, but smaller membrane separator
(the sweep separator) has been added. Reformate leaving the steam
superheater is directed to the sweep separator first then through a
water-gas shift reactor and then to the same membrane present in
FIG. 1. Steam is directed from the small vaporizer into the
hydrogen side of the small membrane separator where it picks up
hydrogen and transfers it to the HDS steam condenser where the
water is mostly condensed out of the system leaving only high
pressure hydrogen in the stream to the HDS reactor.
Some examples of benefits of this approach include the following:
The HDS system can operate at a pressure higher than the reformer
because the pressure is determined by water flow through the small
HDS separator and is independent of the reformate pressure. Clean
fuel can be directed to the reformer without condensation. When the
clean fuel/hydrogen mixture is routed directly to the reformer as
shown, the reformer pressure and HDS pressure are related through
line pressure drop. The excess hydrogen used for desulfurization is
not "wasted" on combustion but is returned to the high pressure
stream for use in the fuel cell. The hydrogen mixed with the
vaporized fuel as it enters the reformer reduces the potential for
carbon formation. There is minimal potential for COS formation as
CO.sub.2 and CO are not present in the HDS reactor feed stream. The
shift reactor following the initial membrane serves to replenish
the hydrogen removed from the reformate yielding better overall
hydrogen production compared to other systems. The use of high
purity hydrogen may enable the processing of more difficult fuels
(e.g. diesel, naval fuels) than can be processed with reformate.
The use of high purity hydrogen may beneficially change the
composition of the fuel by hydrogenating and breaking some aromatic
ring structures. These benefits apply to either a PEM, SOFC, or
other fuel cell system if the fuel is routed directly from the HDS
system (ZnO bed) to the reformer. For the case where the fuel is
condensed after the ZnO bed, the benefits of the second, third and
fourth bullets do not apply to either system.
FIG. 3 shows another fuel processing system that includes a sweep
membrane separator according to the invention. In this system the
fuel is condensed and then supplied to a fuel cell for normal
operation, not just for start-up. That is, the fuel cell system can
be operated in the condensed fuel mode. Such an approach may be
appropriate for systems that are frequently started and stopped. It
may also be useful where clean, desulfurized fuel is needed for
other applications so that the fuel cell system serves not only to
produce electrical power but to supply clean fuel for other
uses.
FIG. 4 shows a fuel processing system for a solid oxide fuel cell
that includes a sweep membrane separator according to the
invention. In contrast to the systems shown in FIGS. 1-3, this
system does not include a large membrane separator or a water-gas
shift reactor. Instead, the reformate is routed directly from the
sweep separator through a control valve to the SOFC stack. FIG. 4
shows that fuel is not condensed before being directed to the
reformer but such a system may also be operated in a manner similar
to FIG. 3 where the fuel is condensed and then pumped into the
reformer.
Further aspects of the invention are described below, some of which
are illustrated in one or more of the above-described figures.
The invention relates to a fuel pre-processing system including: a
hydrodesulfurization (HDS) reactor operating at 200 to 500 psig and
200 to 500 C; a sulfur compound absorbing reactor operating at 200
to 500 psig and 200 to 400 C; a supply of hydrocarbon fuel possibly
containing sulfur bearing material (e.g. benzothiophene); and a
supply of hydrogen at a pressure equal to or greater than the HDS
operating pressure.
The above-described fuel pre-processing system may include one or
more of the following features in certain embodiments: a. The
sulfur compound absorbing reactor contains zinc oxide. b. The HDS
reactor contains a selective desulfurization catalyst such as may
be known in the industry. c. The hydrocarbon fuel and hydrogen are
mixed before the HDS reactor. d. The output stream is a mixture of
clean fuel, hydrogen, and possibly secondary compounds such as
partially hydrogenated fuel or secondary decomposition compounds
from the original fuel.
The invention relates to a fuel processor including: a fuel
preprocessor as described above, the clean fuel output being
directed to the reformer without being condensed; a reforming
reactor; a primary water vaporizer (steam generator) to supply the
reformer; a secondary water vaporizer (steam generator) to supply
the sweep separator; and a sweep separator to provide hydrogen to
the fuel preprocessor described above.
The above-described fuel processor may include one or more of the
following features in certain embodiments: a. The reforming reactor
is supplied by a burner to provide heat for reforming, the burner
operating on excess reformate, off-gas from the HDS process, or
other source. b. The reforming reactor is a microtech type reactor.
c. The reforming reactor is designed for high heat transfer from
the combustion gases. d. The primary and secondary vaporizers are
different sizes. e. The primary and secondary vaporizers are
designed for high heat transfer from the combustion gas. f. The
primary and secondary vaporizers are located downstream (in the
combustion gas) of the reforming reactor. g. The reformate leaving
the sweep separator is provided directly to a fuel cell (e.g. SOFC
or high temperature PEM). h. The fuel processor includes a water
gas shift reactor after the sweep separator. i. The fuel processor
that includes a main separator after the shift reactor. j. The
hydrogen output of the membrane separator is directed to a fuel
cell (PEM, SOFC, or other type). k. The retentate output of the
membrane separator is directed to a burner to provide heat for
reforming. l. Vaporized fuel is used as the sweep gas. m. The fuel
processor includes a secondary burner to heat the system for
start-up.
The invention relates to a fuel processor including: a fuel
preprocessor as described above, the preprocessor output being
directed to a fuel condenser to remove clean fuel from the
non-condensable gas; a reforming reactor; non-condensable gases
from the clean fuel condenser being routed to the burner to provide
heat for the reforming reaction; part of the clean, condensed fuel
being provided to the reformer for operation (start-up or normal);
and part of the clean fuel potentially being supplied to another
device or storage location to be used by other devices.
The invention relates to a fuel processor including: a fuel
preprocessor as described above, some portion of the clean fuel
output being directed to the reformer without being condensed, and
some portion of the clean fuel output being directed to a fuel
condenser for storage or distribution; a reforming reactor; and a
sweep separator to provide hydrogen to the fuel preprocessor.
The invention relates to a fuel processor including a
hydrodesulfurization reactor and a reforming reactor, the fuel
processor operating at a pressure lower than the
hydrodesulfurization reactor to allow non-condensed clean fuel to
be supplied directly to the reforming reactor. In certain
embodiments, the fuel processor operates at a pressure of 150-300
psig.
The invention also relates to a fuel processor including a
reforming reactor, and a sweep membrane separator, where the sweep
membrane separator is used to increase hydrogen content of
feedstock prior to reformation. In some embodiments, the use of the
sweep membrane separator positively affects catalyst lifetime and
performance.
Referring now to FIG. 5 and the following paragraphs, the sweep
membrane separator and its function are described in more detail.
As mentioned above in the Background section, Battelle has
developed an HDS system that works with a hydrogen-containing
gaseous mixture such as a reformate. Although the newly developed
HDS system will work with mixed gases, the system requires high
hydrogen partial pressures in the feedstock. We have found that the
performance of such a system can be further enhanced through the
use of gas streams that consist almost entirely of hydrogen if the
hydrogen can be obtained at an appropriate pressure. The sweep
membrane separator can be used for supplying hydrogen at high
pressure for use in HDS systems and other applications.
The ability to supply pure hydrogen to the HDS system instead of
reformate greatly simplifies system design and increases the
effectiveness of the desulfurization process. Also, when supplying
hydrogen to the HDS system instead of reformate, the reformate
pressure can be controlled relatively independent of the HDS
pressure, partially decoupling the two systems and reducing control
complexity.
As shown in FIG. 5, the sweep membrane separator includes an outer
housing of any suitable design, which is constructed to withstand
the pressures associated with the operation of the separator. The
sweep membrane separator also includes a membrane extending across
the interior of the housing and dividing it into two sides,
hereinafter referred to as the retentate side (the left side in
FIG. 5) and the permeate side (the right side). The membrane is
selectively permeable to hydrogen or another selected gas depending
on the particular application. The illustrated membrane selectively
allows the permeation of hydrogen molecules across the membrane
from the retentate side to the permeate side. Membranes that are
selectively permeable to hydrogen can be made from palladium alloys
or other suitable materials. The membrane is provided with
sufficient surface area to allow a desired rate of diffusion of the
hydrogen through the membrane.
In operation, a mixed gas stream including hydrogen or other
selected gas enters the sweep membrane separator and contacts the
retentate side of the membrane. For example, when the sweep
membrane separator is used in a fuel processing system the mixed
gas stream may be a reformate. The membrane selectively allows the
permeation of hydrogen across the membrane to the permeate side. At
least part of the hydrogen separates from the mixed gas stream and
passes through the membrane to the permeate side.
Because the hydrogen permeation rate is proportional to the partial
pressure difference across the membrane, the hydrogen is withdrawn
from the permeate side at a lower partial pressure than the
retentate side. In certain embodiments, the hydrogen pressure on
the permeate side is 1/20 to 1/100 of the hydrogen partial pressure
on the retentate side. For example, when the mixed gas stream is a
reformate entering the retentate side of the sweep membrane
separator at 300 psig, the hydrogen which has passed through the
membrane to the permeate side may be at a pressure of about 5 to 15
psig.
As described above, an HDS system requires an elevated hydrogen
pressure to operate, for example a hydrogen pressure of about 270
psig or greater. To produce hydrogen at elevated pressure for use
in HDS systems or other applications, the sweep membrane separator
increases the pressure of the hydrogen that has passed through the
membrane. This is accomplished by the use of a sweep gas at high
pressure that enters the sweep membrane separator and sweeps the
hydrogen from the permeate side of the membrane, thereby
compressing the hydrogen. In certain embodiments, the hydrogen
pressure may be increased to a pressure of about 200 psig or
greater, and preferably about 250 psig or greater. For example, we
have found that hydrogen may be produced at pressures of 250 psig
or greater when extracting from a 300 psig reformate stream
containing only 40% hydrogen (hydrogen partial pressure of about
120 psig in the reformate).
Because the sweep gas sweeps away the hydrogen from the permeate
side, the hydrogen partial pressure difference driving hydrogen
across the membrane continues to exist even though the absolute
pressure on the permeate side of the membrane may be higher than
that on the retentate side.
Any suitable sweep gas can be used with the sweep membrane
separator. For example, the illustrated embodiment uses steam as
the sweep gas. However, other gases can be used which are easily
separated from hydrogen including other condensable gases such as
refrigerants and heat transfer fluids. In one possible embodiment,
vaporized fuel is used as the sweep gas either alone or in
combination with another carrier gas.
In the illustrated embodiment, the steam hydrogen mixture exits the
membrane separator and can then be cooled, the water condensed and
removed, and the hydrogen reheated prior to mixing with the sulfur
bearing fuel to provide a high purity hydrogen/sulfur-bearing-fuel
stream to the HDS system. The temperature of the water condenser
can be adjusted to allow the presence of some water into the HDS
system, which may or may not be beneficial in supporting the
reaction.
In short, the steam sweep membrane separator uses a
hydrogen-selective membrane to supply hydrogen to a desulfurization
process. The approach is to use steam to sweep hydrogen from a
membrane separator followed by condensation of some or all of the
water to provide hydrogen at a pressure elevated above the hydrogen
partial pressure in the reformate, and therefore provide high
purity hydrogen to a desulfurization process at a rate that can be
adjusted by the rate of steam flow. Water flow rate is ultimately
used to determine hydrogen flow rate on the permeate side for a
given amount of hydrogen in the retentate at a given pressure.
The sweep membrane separator can be used in many different
applications in fields such as automotive, chemical, and energy.
For example, use of the separator in fuel cell systems can simplify
and reduce the size of the systems. This approach has the potential
to process heavy fuels in a small, compact configuration not
achievable using other technologies. The pressurized hydrogen
produced by the sweep membrane separator is beneficially used in an
HDS system as described above. It may also be supplied directly to
fuel cells operating at elevated pressure.
Although the sweep membrane separator has been described in detail,
more generally the invention provides a method of compressing
hydrogen without the use of mechanical compressing equipment. The
method involves providing hydrogen, and using a gaseous sweep
stream to compress the hydrogen. In certain embodiments, the sweep
stream comprises pressurized steam. The method can be performed in
relation to the steam sweep membrane separator, but it could also
be performed in other ways.
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